Strings of drill pipe or hollow rod are frequently lost down a well. They are lost by breakage of the pipe, or by unintended unthreading at the joinder of two pipe sections. In either event, the downhole portion of the string is out of direct reach from the surface, and it is necessary to retrieve it with the use of a retrieval tool.
The lost portion can involve a variety of problems, none of which can be directly observed from the surface. For one, its upper end may lean against the casing, so that a retrieval tool which operates only at the well axis cannot find it or grab it. For another it may be so strongly retained in the well that the tool cannot withdraw it. It is then necessary to disengage the tool. If the tool is so strongly engaged to the string that it cannot separate from it, an already miserable but potentially correctible problem becomes nearly unsolvable. For another, to provide gripping means which are readily disengaged usually involves insufficient grasping strength, and actuating means which is so complicated as to be unreliable.
It is an object of the present invention to provide a retrieval tool for engaging the free end of a string whether the end is initially centered in the well or not.
Another object of this invention is to provide a simple but reliable gripping means which can readily be disengaged from the string if it becomes necessary to separate them.
Another object of the present invention is to provide means for removing sediment ahead of the retrieval tool so it can reach and reliably engage the lost portion.